Brake System - Audi A4 2001 Owner's Manual

Brake system

The new Bosch ESP 5.7 is introduced in the
Audi A4. The ESP 5.7 is distinguished by the
following special features:
– The hydraulic unit and control unit form a
single unit.
– The charging pump (actuation of ESP
hydraulic pump V156) is discontinued.
– A brake assistant is included.
Hydraulic modulator
Due to the increased brake fluid viscosity at
extremely low ambient temperatures, the
required delivery rate for the return pump for
ABS V39 could not be achieved without a
charging pump (resulting from the increased
suction resistance in the system).
The purpose of the development of the
ESP 5.7 was to improve the suction of the ABS
return pump so that the charging pump was
no longer necessary.
The charging pump could be discontinued
through the use of a two-stage ABS return
pump, enlarging the cross-section of the
brake lines and the use of a larger-dimen-
sioned central valve in the brake master cylin-
der.
SSP254_094
29